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Question 19M.3.SL.TZ2.bi

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.3.SL.TZ2.bi
Level SL Paper 3 Time zone TZ2
Command term Calculate Question number bi Adapted from N/A
bi.
[Maximum mark: 2]
19M.3.SL.TZ2.bi

A heat pump is modelled by the cycle A→B→C→A.

The heat pump transfers thermal energy to the interior of a building during processes C→A and A→B and absorbs thermal energy from the environment during process B→C. The working substance is an ideal gas.

Calculate the change in internal energy of the gas for the process A→B.

[2]

Markscheme

«use of  U = 3 2 n R T and  p V = n R T to give»

Δ U = 3 2 Δ p V  ✔

« = 3 2 × − 2.5 × 10 5 × 1 × 10 − 3 »

=«–»375«J»  ✔

Another method is possible: eg realisation that ΔU for BC has same magnitude, so ΔU = 3/2 PΔV.

Examiners report

Not very many candidates seem to know the generalised formula ΔU =1.5(P2V2 -P1V1) however many correct answers were seen.

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